Whitlockite is a rare calcium magnesium phosphate mineral found primarily in complex granite pegmatites. Collectors look for its rhombohedral crystal forms, which are often associated with other phosphate minerals in etched cavities or massive pods.
Is this whitlockite?
5-step field checkRun through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.
- 1Test the hardnessTry to scratch whitlockite with a known reference. Whitlockite sits at Mohs 5, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: white.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous to subresinous.
- 4Match the color rangeCompare against the expected color range: colorless, gray, gray white, yellowish, white.
- 5Look at form & habitCrystal system: trigonal. Typical habit: pistolitic, rhombohedral crystals, tabular.
Often confused with
Whitlockite vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside whitlockite
Minerals reported to co-occur with whitlockite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Ca₉Mg(PO₄)₆(PO₃OH)
- Mohs hardness
- 5
- Density
- 3.12 g/cm³
- Streak
- White
- Luster
- Vitreous to subresinous
- Transparency
- Transparent to translucent
- Crystal system
- Trigonal
- Crystal habit
- Pistolitic, rhombohedral crystals, tabular
- Cleavage
- None
- Fluorescence
- Often fluorescent white or yellow under UV
- Rarity
- Rare
- Uses
- Collector, Scientific research
- Host rock
- An uncommon secondary mineral in complex zoned granite pegmatites; in phosphate rock deposits; may be formed in caves from leached guano; in chondrite meteorites
Where rockhounds find whitlockite
Classic worldwide localities
- Palermo #1 mine, near North Groton, Grafton Co., New Hampshire, USA
- Bell pit and Dunton quarry, Newry, Oxford Co., Maine, USA
- Tip Top and Bull Moose mines, near Custer, Custer Co., South Dakota, USA
- Tanco pegmatite, Bernic Lake, Manitoba, Canada
- Table Mountain, Curaçao, and on Sombrero Island, West Indies
- Enderbury Island, Phoenix Islands, Kiribati
Field-hunting tip
Where it forms: An uncommon secondary mineral in complex zoned granite pegmatites; in phosphate rock deposits; may be formed in caves from leached guano; in chondrite meteorites. If you start seeing ludlamite, fairfieldite, triphylite in float, you are in the right ground. Typical habit: pistolitic, rhombohedral crystals, tabular. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify whitlockite?+
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What rocks look like whitlockite?+
What minerals are found with whitlockite?+
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Find whitlockite on the map
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